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watson.fawkes
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| Quote: | Originally posted by Swede
I'm down but not out. I'll find a way to boost efficiency. And the big question, what in the HELL hapened to my cathodes?  |
Here's my guess, written as a series of
questions.What the difference in resistance of the solution between the near side of a cathode plate and the far side?
Viewing these two resistances as a parallel circuit, what's the current allocation between these parallel branches?
What does the net current flow look like as a three dimensional vector field?—not just the integral curves, but the magnitude of the
flow.
Assuming the current flow enters the top of the cathode uniformly, what does the current flow look like inside the body of the cathode?
What does scalar field of resistive heat generated by the current within the cathode look like?
Yep, heat warping.
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tentacles
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watson: What would you suggest to alleviate the curling? Drilling the cathode / mesh cathode? Thicker cathode (maybe plus drilling?)? I think we'd all
be amenable to suggestions if you have any. Drilling might alleviate the current differential significantly (as more current would be able to pass
through the back side of the cathodes, rather than almost none). And getting some current to the back side would hydride both parts at a more similar
rate. There's certainly been successes using Ti cathodes, so I won't if this isn't an issue compounded by the welding stress and high temperature of
the cell.. if the cell was at 90C, the cathodes may have been somewhat hotter.
Ti expanded sheet, short of buying it from ebay, and it's rarely sold, is very pricy. McMaster has it for $91/sq ft.
[Edited on 6-11-2008 by tentacles]
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12AX7
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Are you pumping cold solution or hot solution? The better idea would be to pump hot solution so it's not supersaturated. The less preferrable
alternative would be to pump cold solution, but warm it up by snaking the intake hose through the hot cell before reaching the pump. This will not
prevent crystallization along the hose before the liquor inside warms up appreciably.
What does current flow have to do with anything? Water is an excellent conductor of heat and the surface of the titanium will be quite equal to the
liquor's temperature. The core will be warmer, but it won't have much appreciable tangential direction to it -- assuming you're getting at some sort
of front-to-back differential current flow causing this.
What does resistive heating have to do with anything? I don't see how heat alone warps it, especially so little heat. To curve that much, the
material must be physically changed, which is why I suspect hydridation.
Tim
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Rosco Bodine
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Yep if anyone was wondering if it is possible to electrolytically hydridize titanium .....wonder no more.
Embrittlement is the result of deep hydriding , and disintegration to particles of what is mostly hydride is
the end result if the process goes to completion.
Since the hydride is conductive and evidently porous
and corrosive as well, it evidently forms no protective layer against further hydriding, evidently behaving as
a sort of "amalgam"- like composite which behaves as
an absorptive or kinetic conduit for free hydrogen or hydrogen ion.
This hydride formation is really more interesting for its usefulness potential as an anode substrate preparation for doping and baking processes which
may exploit the hydride's thermal decomposition at about 250C to react
with dopants to form an anodically conductive interface layer with the unhydrided and unpassivated titanium of the substrate below.
Clearly it would seem better to use a different material for
the cathodes, something which is not subject to hydrogen embrittlement via electrolytic hydriding.
Maybe silver plated or even silver bearing tin solder plated "tinned" copper or iron would be better as a cathode.
[Edited on 6-11-2008 by Rosco Bodine]
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watson.fawkes
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| Quote: | Originally posted by tentacles
watson: What would you suggest to alleviate the curling? |
First, assume it's heat, and not some other
mechanism. You can eliminate the stress by changing the current & heat distribution, or you can counteract the mechanical force generated.
As to changing the geometry, perhaps the easiest thing to do is to keep the layer structure but have mesh anodes on the ends. The mesh won't have
nearly the same current inhomogeneity.
Even easier, though is to just counteract the bending force. Bond the bottom ends of the cathodes together mechanically. the very simplest way to do
this with two cathodes is to form them as a loop. Alternate, run a bolt between them at the bottom. The advantage of a mechanical solution is that it
addresses the symptom, regardless of what the cause is.
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watson.fawkes
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| Quote: | Originally posted by 12AX7
What does current flow have to do with anything? Water is an excellent conductor of heat and the surface of the titanium will be quite equal to the
liquor's temperature. The core will be warmer, but it won't have much appreciable tangential direction to it -- assuming you're getting at some sort
of front-to-back differential current flow causing this.
What does resistive heating have to do with anything? I don't see how heat alone warps it, especially so little heat. To curve that much, the
material must be physically changed, which is why I suspect hydridation. |
Consider the magnitude of the
current flowing in a cross section of the cathode from near to far side. If there's a near-to-far side disparity, there'll be differential thermal
expansion. What happens at the surface isn't particularly relevant except insofar as it sets boundary conditions for the total thermal flow. You can
have identical temperatures at both surfaces and still have an internal thermal asymmetry.
I'm not at all convinced that the internal heat is all that insignificant. A small force exerted over hours is completely plausible as a source of
creep.
The physical change you require in this hypothesis is inelastic deformation of the cathode, which translates down into rearrangement of crystals in
the bulk metal. To really get an answer I'd have to dig into some material properties (stress-strain curve for the alloy, resistance, thermal
coefficients of expansion and resistance) operation parameters, dimensions, etc. and then spend a bit of time with a simulator to model the current
flow within the cathode. So I'm not going to really get an answer.
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Rosco Bodine
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The idea that warp was caused by heat is a no starter
with me, kind of no way, no how do I believe that and not even maybe. Frankly it seems preposterous .
If that sort of a cross sectional expansion differential
was present , it would be indicative of a laminate like a bimetal strip kind of effect. And if that effect was purely thermally induced to such an
extreme then there is no way titanium would be structurally acceptable for use
in any structural application at all, much less airframes.
[Edited on 7-11-2008 by Rosco Bodine]
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Swede
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Those cathodes were not commercially pure, if that makes a difference, they were a Ti alloy. They were also fairly heavy for sheet, being 0.062" or
1.6mm.
I had used identical cathodes in a previous cell, same spacing, same liquor, same current, with no warpage. The only difference between the setups
was the temperature. The only temp I was measuring was the liquor itself, which I saw to be 90 degrees that morning. In my earlier cells, it was
never more than 60. Something happened between 60 and 90 to warp those cathodes.
I have to believe it is a transformation of the material rather than simply heat warpage. I don't believe the welds had anything to do with it,
either. Ti conducts heat so poorly, when those welds were made, the heat from the welding process probably never made it more than an inch or two
down the cathode, yet the warping is even along the entire length, and it must be an electrochemical transformation, internally.
I'll be happy to try anything you guys want (red heat, etc) and take note of what happens.
For now, I am going to run the big vat in a stand-alone manner. I've figured out a way to use the dosing pump (I found a god timer that will work)
and given the size of this thing, with careful pH control, I believe I can execute MUCH of the chlorate formation using the 6 electron, bulk formation
process. This cell is fairly well insulated on its own, and I believe that I can get the temp up to 60 or 70 at least, and hold it there, due to the
bulk of the liquor.
It would be nice to have mechanical stirring, rather than air-stirring, which will cool the system somewhat.
While this thing is cooking, I am going to rethink the circulation process. Hard CPVC piping, perhaps with foam wrap-around insulation, would be
vastly superior to flex tubing, and the associated hose-barb choke points.
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12AX7
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For asymmetrical current distribution to do that, it would have to be considerable indeed, I'm thinking something like a 45° angle, and there simply
isn't enough current flowing out of that face, in the magnitude that it would have to be flowing (I think hundreds of amperes would be necessary to
raise the core temperature that much) and at a peculiar distribution (current would have to be distributed exponentially from the bottom up).
Titanium does not creep at room temperature, however it does creep at red heat, so the minimum core temperature for this possibility would be on the
order of 600°C. If this were possible in water, the much thinner strap at the top would've completely vaporized quite some time ago! So that's my
final word on heating.
I'm willing to bet that annealing the cathodes at up to red heat will relax them straight again.
Tim
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tentacles
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Re: Silver plated cathode... see http://www.freepatentsonline.com/4186066.html
Yep, that's right, just what we needed.... another ridiculously complicated (I didn't even read past the abstract) Titanium coating process...
I think what we're going to need is more data.. Swede, please keep us apprised of what happens to this cell run. It could be that titanium hydrides
much more readily at higher temperatures. We all know Ti has been used commercially for cathodes in the past - I've come across a few references to
the hydriding phenomenon taking year(s). It could simply be that the water was damn near boiling at the cathodes- Swede, was there seperate
circulation air for the electrode chamber? If not(hell possibly even if so), I'm inclined to conclude it was the extreme environment of the chamber /
probably very low chloride levels etc. I'll have to see it happen again during a normal run before I start looking for other cathode materials and YET
MORE exotic coatings. ;P
We've seen too many successful runs with Ti cathodes for this to be much more than an unfortunate combination of circumstances... unless it happens
again. Then we should probably look at the alloy.
[Edited on 7-11-2008 by tentacles]
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Swede
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Tentacles, I'm inclined to agree. I've not been at this long, but all my Ti cathodes until now have performed very well with no issues.
I never even thought of the extremely low chloride levels in the EC. I wish I had saved some of that liquor separate from the rest to test it and see
what it was. Damn my shortsightedness.  That environment must have been
hellish, yet the MMO held up fine, as far as I could see, so it appears to be good stuff.
@Dann2 - The reason I originally wanted to take the chloride levels very low was for two reasons... first, I wanted to see if there were any ill
effects on this particular MMO mesh. Second, despite the drop in efficiency, most of the work associated with this process is in the setup, teardown,
and collection of the crystals. If I can double the yield on a particular run, even if the efficiency drops a bit, then I think that's a good thing.
I'm into this for the material it produces, ultimately feedstock for a bulk perchlorate setup, for pyrotechnics. The fun of the process, and the
science, is a bonus. I've got a decent collection of analytical reagents to test my purification methods.
As I mentioned, I decided to do a run using just the vat. After a few hours of replumbing, it was ready to go. It's warming up now at 50 amps, and I
did take what I learned and incorporated it into this iteration. I'll get some pics up. This run also will be used to test the integration of the
HCl dosing pump. I like the idea of a dosing schedule that takes place every few hours, rather than a true control loop, and with a bit of effort
and monitoring, I think I'll be able to get very close.
I'm going to do some serious thinking on a circulating system over the next week or two. There are some problems associated purely with the
complexity. A monolithic box is hard to beat, but circulation offers so many possibilities.
One thing definitely needed; some sort of intake screen for the pump. I mentioned that my Hanna dosing pump came with a neat PVDF mesh screen, which
is ideal for a chlorate cell, and they sell it separately. There's no picture on the Hanna site... it is stock number HI 721005 Foot Valve Assembly:
http://www.hannainst.com/usa/prods2.cfm?id=018001&ProdCo...
It comes as a PVDF mesh screen and a check valve, plus a PVDF fitting for 3/8" OD tubing. Something like that, shielding the pump intake, would be
needed. Plenty to think about.
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Rosco Bodine
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| Quote: | Originally posted by tentacles
Re: Silver plated cathode... see http://www.freepatentsonline.com/4186066.html
Yep, that's right, just what we needed.... another ridiculously complicated (I didn't even read past the abstract) Titanium coating process...
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I don't recall suggesting titanium as a cathode material, plated or otherwise, because titanium is known to be vulnerable to embrittlement via
hydriding. Maybe some anode coating schemes seem to be "ridiculously complicated"
but I haven't seen that for cathodes. Graphite or iron or stainless steel or just about anything could be used, and I suggested something
"ridiculously simple" like tinned copper or iron.
| Quote: |
I think what we're going to need is more data.. Swede, please keep us apprised of what happens to this cell run. It could be that titanium hydrides
much more readily at higher temperatures. We all know Ti has been used commercially for cathodes in the past - I've come across a few references to
the hydriding phenomenon taking year(s). It could simply be that the water was damn near boiling at the cathodes- Swede, was there seperate
circulation air for the electrode chamber? If not(hell possibly even if so), I'm inclined to conclude it was the extreme environment of the chamber /
probably very low chloride levels etc. I'll have to see it happen again during a normal run before I start looking for other cathode materials and YET
MORE exotic coatings. ;P |
I'll do some research on that, and see if I can't get back to you with a couple of hundred schemes to select from ....
and I will of course eliminate all of them first which seem
too easy or simple 
| Quote: |
We've seen too many successful runs with Ti cathodes for this to be much more than an unfortunate combination of circumstances... unless it happens
again. Then we should probably look at the alloy.
[Edited on 7-11-2008 by tentacles] |
Hydrogen embrittlement is guaranteed, it is only a matter of time . Now where did that hydrogen go that was making me think we might need a bit of
supplemental hydrogen to
recombine with the chlorine for a recycle loop to hold the pH constant ???? Hmmmmm, wait don't tell me , let me think, now where did that missing
hydrogen go ? I'll leave the riddle for your warped amusement.
Take a look through my sunglasses 
http://www.youtube.com/watch?v=Phzn5wFgaDk
See the light ?
http://www.youtube.com/watch?v=6yWhlSd309A&feature=relat...
referencing the TiH2 thread, here are some parameters
which apply to electrolytic hydriding or avoidance of it. http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...
[Edited on 7-11-2008 by Rosco Bodine]
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tentacles
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| Quote: | I'll do some research on that, and see if I can't get back to you with a couple of hundred schemes to select from ....
and I will of course eliminate all of them first which seem
too easy or simple |
If it doesn't require at least tin (+IV!) nitrate, then clearly it's far too simple and would never work ;P
I just posted that silver-titanium stuff because it turned up on a quick googling, and was at least somewhat similar to your silver plated copper
suggestion. Would silver ions in solution potentially be hazardous? I seem to have some dim recollection of silver perchlorate being bad - assuming it
might form. Silver isn't so expensive that a solid silver cathode couldn't be do-able, either.
As to embrittlement, it IS only a matter of time, but the question is how much time, at more reasonable temperatures and cell conditions?
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Rosco Bodine
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People who have money to burn or who are using electrode assemblies already made of titanium won't have trouble with it under reasonable temperatures
and pH...
as it will last for a very long time. However , it is not the
best choice of material IMO, where a cathode is concerned.
Especially for a high efficiency and high temperature cell
running at high current density titanium would have a vulnerability to embrittlement.
Tin/Silver 96/4 soft solder used as tinning onto copper just seemed like a very easy and inexpensive cathode
which might be convenient, or tinned onto iron should work too. I am thinking in terms also of using plumbing parts for a coaxial electrode with a
pumped flow through electrolyte ....and these materials are available. The cell temperature would be easily regulated using such an arrangement and
it would solve other problems. The anode would be a solid rod form in the center axis of the cylindrical assemblyand the inside walls of the tubular
housing would be the cathode.
The whole matter with regards to tin nitrate is going to be a matter of experimentation by me when I can get to it.
I documented pretty well what should be looked into there. Did you ever try using ammonium carbonate or bicarbonate for the neutralization of a
stannic chloride
to precipitate the stannic acid which should be useful for obtaining the nitrate.....and that not work as reported in the literature ? Or any of the
other reported methods ?
It's not some emotional deal with me what chemical reactions are reported or contemplated...this is simply science to me. But with all the literature
which has described tin nitrate and its derived sols...I find it unlikely
that it is all just somehow a bunch of bullshit that has been published about this for the past couple of hundred years. It would be my guess that
maybe it is sensitive
reaction and isn't workable except under a narrow range of conditions which simply are being missed by folks who are dismissing it out of hand. There
are other valid reactions which I have seen that are similarly sensitive,
though not impossible to duplicate.
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dann2
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Hello Folks,
The bent cathodes look amazing. Between cathodes bending and anodes getting eaten away by parasitic currents, I think we should throw in the towel and
end this thread now (and the Chlorate/Perchlorate making too).
Swede:
Just carry on using the warped Cathodes + anode. The bend is not going to have much [none] effect on the system. A bit of uneven current distribution
on the anode that is not going to have any significance at all. It's not worth bothering to try to straighten them.
I would be inclined to guess (as Tim said) that it is some sort of Hydriding effect. I have used Ti Cathodes for months without any bending. The
temperatures were not any higher that 70C and it was grade one. Some of the runs went from Chloride to (almost pure) Perchlorate , ie. no or very low
Chloride during a part of the run.
Would perhaps Al have leached out of the alloy on the back side of the Cathodes (Current density low, and may not have been properly cathodically
protected on that side) and this caused bending. (Total guess).
Tentacles has put it well. Basically you have discovered a new way to bend Ti without at boiling water temperatures. I wonder if you had to leave the
whole lot here for a day or so would the Ti have warped into a circle.
I have seen pieces of Ti strip warp when there were placed in a furnace at bright Orange heat for about 1.5 hours. The strips were only supported at
each end and were about 5 inches long. Trying to make Magnetite anodes...................
I have read that Ti Cathodes 'only' last for two years (that would be 24/7) in industrial set ups. The Ti would be Grade 1, 2, 3 or 4, ie. No Al
(Ullman page 30). High temps. seem to help their downfall.
Hydrogen embrittlement being their downfall. It is hard to believe that the Ti would start to fall apart in the cell but it must do just that.
If using a two compartment set up, one for electrodes and one for Chemical Chlorate formation, the electrode compartment can be at a lower temp. that
CCF Chamber.
It is a pity to use any other type of Cathode in an MMO set up where one of your goals is to have spotlessly clean Chlorate coming from the cell. Ti
will not reduce Chlorate which is another advantage.
Iron will corrode without Chromate, so will Nickle. You could try stainless steel of course. Don't think it will corrode as long as you cell is
running (Cathodically protected). Graphite can also be used but you will get some black mess.
Most if not all other materials will corrode if you get a power outage especially if you have no Chromate present.
You could consider (since you appear to have a Hector of the stuff) using MMO for the Cathode.
If you want simplicity use Platinum! (both anode and cathode). Slab shaped pieces are good!!
Silver Perchlorate has been reported to explode on its own. Since Silver Chloride is insoluble, Silver it's not going to stay in solution. If using Na
in the cell it will stay at the bottom. When using K you will be more likely to have tiny amounts of Silver Chloride in the K Chlorate.
I am inclined to keep Copper and Silver miles from Chlorate/Perchlorate that is being used for Pyro stuff.
Will the intake screen that you speak of not be inclined to plug up if crystals form?
I like the description of the reactions;
The 6 electron route (pH control).
The 9 electron route (no pH control).
Sums it up well.
There is more figures for acid need per ton Sodium Chlorate in Ullman page 27 (below).
HCl (33 %, ) 35, 30, 33 and 50 KG's per ton Na Chlorate.
Ullman (page 9) also mentions keeping CD high on cathodes to decrease hypochlorite reduction. Since you are not using Dichromate this is something
you may wish to think about in rev. 3! It is a somewhat minor issue I think.
Dann2
[Edited on 8-11-2008 by dann2]
Attachment: ullman.pdf (819kB)
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Rosco Bodine
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| Quote: | Originally posted by dann2
Hello Folks,
The bent cathodes look amazing. Between cathodes bending and anodes getting eaten away by parasitic currents, I think we should throw in the towel and
end this thread now (and the Chlorate/Perchlorate making too).
Dann2 |
Aw shucks Dann2 knock it off with the "negative waves"
You know when there's a light at the end of the tunnel...
it's not always just the train coming.
http://www.youtube.com/watch?v=KuStsFW4EmQ
If you are concerned about the Sn/Ag 96/4 then try instead Sn/Sb 95/5 or even Sn/Pb 60/40. Some of Sn/Bi alloys might be good also. 316 stainless
would probably be good too.
[Edited on 8-11-2008 by Rosco Bodine]
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Swede
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I attempted to bring one of the cathodes to red heat without ruining the plastic, but it was difficult to achieve an even heating, even with two
propane torches. I don't have an oxy-acetylene rig, so I really couldn't do a proper job of it, nor could I hold it at a high heat for any length of
time.
Results: A very small but percpetible straightening. What conclusions can be drawn from that, I have no idea.
A tinned copper cathode would not be hard to do. The best way would be a pot full of molten alloy. Prep a Cu pipe section with a hydrochloric or
other acid dip to flux it, then dip into the pot. I'm sure it could be done by hand as well with a handful of solder wire and a propane torch.
Question for you guys on my HCl dosing setup - the dosing pump works very well, and the concept of having a simple dosing schedule, vs. a true control
setup, seems to be bearing fruit. The larger the cell, the better it works, due to the inertia of the system. Example: My 25 liter cell measures,
say, 7.6 pH. I turn the pump on and count 10 pulses of the diaphragm, which equals 10 ml of acid. One hour later, the pH is 7.4. In this way, I
zero'd in on 6.8, and once there, it takes many hours of running for it to begin to creep back up.
In this picture, you can see the injection nozzle on the left side of the lid. It is the one with the heavier Tygon tubing, leading to a
cream-colored PVDF check valve fitting.
A schedule of 4X per day, dosing 20 to 30 ml into this 25 liter system, would keep the pH between 6.4 and 7.4 with ease. All I need now is a good
timer. I am trying a consumer Intermatic timer, but I am not happy with it. I don't trust it, and the thought of it sticking ON is not a good one.
Is there such a thing as a "lab-grade" timer that you can program? Anyone have any experience with such a device? If so, I'd like to hear about it.
Thanks!
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Rosco Bodine
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There are different levels of solutions as process timers depending on how pretty and fancy you need or want.
Lawn sprinkler irrigation timers should be easily adaptable.
Aquarium timers are probably the closest thing to what you need as a process controller.
http://cgi.ebay.com/3-Sockets-Digital-3680W-Programmable-Tim...
As for the alternatives...
there's fancy (and expensive) top of the line stuff
http://www.omega.com/pptst/PTC-15.html
there's improvised and cheap stuff
http://www.hackersbench.com/Projects/3bucktimer/
[Edited on 9-11-2008 by Rosco Bodine]
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dann2
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Hello Swede,
Just wondering if you are getting a good mixing in the tank with the air pumping. (I presume you are stll stirring with air).
Is there much of a difference in temperature between the top and bottom of tank?
One safety feature you could implement is to have only approx. 50ml of acid in the dosing container so that 50 ml is the max. that could be added if
a fault developes.
Dann2
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dann2
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Hello,
Though I would post this paper here.
It seems to say that you get max. erosion for a Graphite anode when pH is around neutral!!! but the set up they use is not comparable to a Chlorate
cell. They have a continous flow of salt water and do not allow any Hypochlorite (let alone Chldorate) to build up in there cell.
Dann2
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Swede
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Rosco B, thank you for those options. I didn't even think of an irrigation sprinler. Initially I thought 1 minute ON would be too much, and most
consumer timers cannot do less than 1 minute, but I've seen a one minute on will dose about 12 ml of liquid, and this is working well. For a smaller
system, volume-wise, you'd need either a smaller pump, weaker acid, or less than 1 minute of dosing; otherwise, I think you risk overdose of HCl.
Dann2, I cannot measure the temperature in different parts of the tank. On an older system of mine, very tall and skinny, the air mixing worked well
to achieve uniform temperature. Since this one is bulkier, I can only hope it will work as well. I do have two pumps running. Aquarium pumps are
pretty weak, and it's worth buying a powerful one vs a low-end unit. I have seen the tubes get clogged with crystals before. The air flow drops the
temp and there's a localized crystallization that can jam it, but a strong pump, when turned up, blows the crystals out, and then I can dial it back.
I'm running these at maybe 1/3.
I measured chloride today, and it is down to 114 g/l, so there's still a way to go with this run. Samples drawn for pH, when they cool, crystallize a
significant mass of chlorate crystals, so there's no doubt it's working as it should. 60 amps is too low for this system, but that is all my constant
current supply can do. I want to run CC to check the efficiency. The voltmeter is hovering around 4. I've got a couple of very heavy 5V supplies
that would easily do 80 to 120 amps, but I'll save those for later runs. Temperature though will be a problem. The tank is PVC, not CPVC, and I am a
bit concerned when the temp gets over 60 or 70. It's a struggle between materials, and a desired process temp of 80 to 90. I wonder what commercial
tanks are constructed of? Ti, maybe? That would not be economical for quantities measured in Tons. I would gladly buy a case of beer for the
workers if I could get a tour of a plant.
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Rosco Bodine
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There are various digital timer and analog timer controlled
relay circuits , and counter derived hybrid sorts of circuits
which can be put together as relatively simple projects
from cheap IC's using point to point handwiring on perf board. The 555 timer IC is an example of a single chip
solution which works something like the delay windshield wiper circuit in a car .....where you can set the interval
for cycling and the duration of the "on time" between cycles as well, using a couple of potentiometers. I have thrown together a few of these little
timer projects as
"process controllers" and they do the job if you can't find something already built. Years ago there wasn't so much cheap digital programmable ready
to use timers, so we improvised, even before the 555 came out, using simple transistor timed relays as process cycle timers.
You might want to look at "band heaters" and some metallic sections of piping and fittings, with some thermostat controls, if you go with a pumped
system,
you can then control where crystallization occurs in
a way that is parallel to what is done for the large scale industrial cells.
A thermally controlled current limiter on the cell itself would be a good idea too to prevent things from getting out of hand .
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Swede
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I've really been absorbing a lot of great info from you guys - I appreciate your expertise.
I've been wondering how they do it commercially. I understand it's an open system... the liquor flows in, get's processed in several cells, then it
flows out for collection. I know they use sodium salts, and there is NO crystallization until they want it to happen. The vast bulk is retained as
sodium chlorate for the bleaching of paper and wood pulp, and some of it is converted to potassium and other chlorates.
I'm picturing a giant vat of saturated sodium chlorate + byproducts... how do they extract the sodium chlorate from the liquor, and importantly, how
do they clean it up?
Using potassium salts is problematic. Those crystals tenaciously form everywhere there is the slightest temperature gradient. I really, really need
to think about using sodium instead, and execute a double decomp to obtain the potassium product.
I have some very basic questrions... Given say 4 liters of sodium chlorate laden cell liquor, which will be mixed with chloride, chlorite, etc ions,
how does one know the correct quantity of KCl to add? If you can determine quantitatively the chlorate ion concentration, then it'd be easy, but
determining chlorate concentration is not a simple thing.
After adding the KCl (hot, saturated solution, I assume) the KCl falls out. What remains in the solution is a mix of sodium, any excess potassium,
and all the chlorinated ionic species, a real hash. Does this liquor then get recharged with chloride, and resused, despite the possibility of
potassium in the mix?
My own lack of understanding of the metathesis process, and the ease and cleanliness, is why I use potassium chloride at the beginning, but it has
huge drawbacks that I need to overcome. Frankly I do not thing a pumping/recirculating system is possible using potassium chloride... it MUST be
sodium. Thoughts?
This 25 liter cell has had 50 amps through it since Saturday. Chloride levels started at 125 g/l and are now down to 95 g/l, for a yield (so far) of
30 * 25 = 750 grams of chloride converted, meaning there is 2,627 grams of potassium chlorate in there. I'll probably run it to 60 grams per liter,
so another day or two at least.
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watson.fawkes
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| Quote: | Originally posted by Rosco Bodine
There are various digital timer and analog timer controlled
relay circuits , and counter derived hybrid sorts of circuits
which can be put together as relatively simple projects
from cheap IC's using point to point handwiring on perf board. |
These days, the single best solution to this
class of problems is the Arduino microcontroller. It's got a very straighforward hardware interface and is integrated with a handy programming system
(called Processing). I've done software for a long time (including embedded systems) and this is easily the best entry point I've ever seen.
More generally, any micro-scale industrial process, in the present example, chlorate manufacture, is going to need an electronic sensor and control
system. I consider it just a cost of entry. Sure, it's possible to do the reactions without such control, but if you're thinking about manufacturing
proper, even at a small scale, this is definitely the right way to go, for safety as well as efficiency. Arduino is an open-source hardware project.
It's caught fire in the DIY crowd and lots of accessories are available for it. New and assembled, it's about 40 USD. http://www.arduino.cc/
These days when I consider a project, I start by counting sensors.
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12AX7
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| Quote: | Originally posted by Swede
I have some very basic questrions... Given say 4 liters of sodium chlorate laden cell liquor, which will be mixed with chloride, chlorite, etc ions,
how does one know the correct quantity of KCl to add? If you can determine quantitatively the chlorate ion concentration, then it'd be easy, but
determining chlorate concentration is not a simple thing. |
Ah, but it is. Take a known volume of solution, add an excess of concentrated KCl solution and wait for it to precipitate. Filter, wash, dry and
weigh the precipitate (or guess by experience). Now add enough KCl solution to drop 50 to 75% of the chlorate in solution. What remains in solution
will reduce the solubility of potassium a bit. Let temperature drop to room temp (or below, if possible) and you'll have 99% or so yield based on
potassium.
There's nothing wrong with sodium chlorate, either. It's really easy to handle. Doesn't even seem too hygroscopic in bulk, I've got pounds of it
sitting open in the basement air and it didn't liquify at all during the summer. (The exposed sodium perchlorate, on the other hand, remained quite
fluid.)
Tim
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